refactor: keep attr-only statements and cloned lets printable #1457
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fw-immunant
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Nov 17, 2025
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Seems reasonable. Is there an easy way to observe the change in behavior? It would be nice to have a test case if possible.
ahomescu
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Nov 19, 2025
| /// Pick the span we should attach to a freshly minted statement. | ||
| /// | ||
| /// We want new statements produced by transforms such as `sink_lets` or | ||
| /// `fold_let_assign` to retain the source span of the code they were cloned |
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Could we just fix the transforms then? Why couldn't they pass in the spans?
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@ahomescu @fw-immunant I'm trying a different approach in #1469 based on this comment. If that looks good, I'll merge it and close this one
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Several transforms (
sink_lets,remove_redundant_let_types) were panicking whenever the rewrite engine had to reparse snippets that no longer looked like full Rust statements.Two cases showed up when testing:
#[derive]lines, the transform temporarily splices only the attribute text (for example just#[derive(Copy, Clone)]) while the enclosing struct body is rewritten at a higher level. Rust’s parser refuses that input, soPrintParse<Stmt>panicked before recovery finishedletbindings inherit the builder’s defaultDUMMY_SP, so pretty-printing emits an empty string even though the original code had a real initializer. The AST/text round-trip fails and subsequent rewrites abortThis PR:
PrintParse<Stmt>up front, reparses them by temporarily appending a dummy struct, and returns aStmtKind::Emptythat carries the combined attribute span, which keeps the rewriter from panicking while the surrounding struct/item is printed elsewhereDUMMY_SP. Newly cloned locals/exprs retain their original source ranges, sorewrite_at_implcan pull real snippets instead of an empty buffer